manage process in linux

1) how to show all the processes running: top
2) how to kill a process ? for example firefox ?
ps -aux |grep firefox ----can find the job id of firefox
kill id
3) how to run a job in background, even i have logged out of the system:
screen
launch your program
ctl-A then ctl-D
Now you have launched your program in background, and it will run while you log out the system.
If you want to check the run, use "screen -r"
if you want to exit from screen, use "exit"